Systems, methods and devices for anatomical registration and surgical localization

ABSTRACT

Systems, methods and devices are disclosed for use in electronic guidance systems for surgical navigation to determine the relationship between the three-dimensional coordinates of an anatomy of a patient and those of an electronic guidance system. These coordinates are required to assist in the determination of the angles with respect to which components, such as, an acetabular prosthesis, are inserted into a body of the patient. In one such example, during hip replacement surgery, a surgeon receives guidance of how to place an acetabular prosthesis in the body of the patient, specifically in the pelvis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application No.62/072,041 titled “Systems, Methods and Devices for AnatomicalRegistration and Surgical Localization” and filed on Oct. 29, 2014, theentire contents of which are incorporated herein by reference.

This application claims priority to U.S. provisional application No.62/072,030 titled “Devices including a surgical navigation camera andsystems and methods for surgical navigation” and filed on Oct. 29, 2014,the entire contents of which are incorporated herein by reference.

This application claims priority to U.S. provisional application No.62/084,891 titled “Devices, systems and methods for natural featuretracking of surgical tools and other objects” and filed on Nov. 26,2014, the entire contents of which are incorporated herein by reference.

This application claims priority to U.S. provisional application No.62/072,032 titled “Devices, systems and methods for reamer guidance andcup seating” and filed on Oct. 29, 2014, the entire contents of whichare incorporated herein by reference.

FIELD

The present specification relates to systems, methods and devices foruse in registration of an anatomy of a patient during surgery, forsurgical navigation.

BACKGROUND

A human hip joint is a ball and socket joint comprising the head of afemur bone (femoral head) located in an acetabulum of a human pelvis.During total hip arthroplasty (THA), the hip joint of a patient isreplaced with prosthetic components. The surgical procedure involves thesurgical excision of the head and proximal neck of the femur bone andremoval of the acetabular cartilage and subchondral bone. An artificialcanal is created in the proximal medullary region of the femur, and ametal femoral prosthesis is inserted into the femoral medullary canal.An acetabular component or implant is inserted proximally in theenlarged acetabular space.

One of the most important aspects of THA is ensuring proper alignment ofthe acetabular component or implant with respect to the pelvis.Alignment of the prosthetic components has typically been performedrelying solely on a surgeon's judgment of the spatial location of theprosthetic components. Studies have shown that failure to properly alignthe acetabular component or implant with the pelvis may lead topremature wear, propensity to dislocate and patient discomfort. Surgicalnavigation systems can assist surgeons in providing guidance in theplacement of the prosthesis in the body of the patient to improveclinical outcomes.

BRIEF SUMMARY

This specification describes methods, systems and devices used toregister the body of the patient to an electronic guidance system forsurgical navigation. During surgery guided by electronic navigation, asurgeon typically has to determine a correlation between the coordinatereference frame of a patient and that of the electronic guidance systemfor surgical navigation. This allows the surgeon to use his/her clinicaljudgment when viewing the measurements and deciding the final placementof objects, such as a hip prosthesis, in the body of the patient. Thesurgical navigation system needs to know the correlation so thatmeasurements can be provided in one or both coordinate frames.

There is disclosed a system to provide intra-operative guidance duringTHA. The system comprises: a sensor configured to attach to an anatomyof a patient, positioned in a known orientation with respect to gravity,and comprising an optical sensor to generate optical measurements and aninclinometer to generate inclination measurements; a target configuredto provide positional information to the optical sensor, the opticalsensor generating the optical measurements using the positionalinformation in up to six degrees of freedom; a device attached to thetarget, the device having a shape defining at least one axis, whereinthe at least one axis is in a known positional relationship with thetarget; and an intra-operative computing unit in communication with thesensor. The intra-operative computing unit is configured to: measure adirection of at least one axis using the optical measurements from thesensor and the known positional relationship between the target and thedevice; measure a direction of gravity based on the inclinationmeasurements; and construct a registration coordinate frame to registerthe anatomy of the patient during surgery to provide surgical navigationbased on the direction of gravity, the direction of the axis and theknown orientation of the patient with respect to gravity. Theintra-operative computing unit is further configured to calculate, inreal-time, a difference in the optical measurements in at least onedegree of freedom provided by the optical sensor with respect to theregistration coordinate frame and to provide the difference for displayby a display unit. A sensor configured to attach to an anatomy of apatient, the anatomy being a pelvis. The device may be removablyattached to the target.

There is disclosed a medical navigational guidance system wherein theintra-operative computing unit is further configured to construct thecommon frame of reference using a rigid mechanical relationship betweenthe optical sensor and the inclinometer. The intraoperative computingunit is further configured to construct the registration coordinateframe using redundant measurement information wherein the redundantmeasurement information is used to compute a metric representing theconsistency between the inclination measurements and opticalmeasurements received from the sensor; and provide the metric to adisplay unit for displaying to a surgeon. The sensor is configured togenerate optical measurements and inclination measurements relative to acommon frame of reference.

There is disclosed a system for providing navigational guidance duringTHA. The system comprises: a sensor configured to attach to an anatomyof a patient, comprising an optical sensor to generate opticalmeasurements and an inclinometer configured to generate inclinationmeasurements; a target configured to provide positional information tothe optical sensor, the optical sensor generating the opticalmeasurements using the positional information in up to six degrees offreedom; a probe attached to the target, the probe having a tip, whereinthe tip is in a known positional relationship with the target; and anintra-operative computing unit in communication with the sensor. Theintra-operative computing unit is configured to: determine a location oftwo or more anatomical features of the patient, the features lying onthe anterior pelvic plane of the patient, using optical measurements ofthe sensor and the known positional relationship between the target andthe tip of the probe; calculate a direction of at least one axis definedby the location of the two or more anatomical features; and construct aregistration coordinate frame to register, during surgery, the anatomyof the patient based on the direction of gravity and the direction ofthe axis. The intra-operative computing unit is further configured togenerate a secondary registration coordinate frame by localizing threeanatomical features on the acetabular rim of the patient. The system isconfigured to provide navigational guidance based on the registrationcoordinate frame and the secondary registration coordinate frame. Asensor configured to attach to an anatomy of a patient, the anatomybeing a pelvis. The probe may be removably attached to the target.

There is disclosed a computer-implemented method for a medicalnavigation guidance system capable of: measuring, by at least oneprocessing unit, a direction of gravity using a sensor, the sensorcomprising an optical sensor and an inclinometer, attached to an anatomyof a patient positioned in a known orientation with respect to gravity;measuring, by at least one processing unit, a direction of an axis of adevice, the device having a shape defining at least one axis usingpositional information in up to six degrees of freedom provided by atarget to the optical sensor, and a known positional relationshipbetween the target and the device; and constructing, by at least oneprocessing unit, a registration coordinate frame to register, duringsurgery, the anatomy of the patient based on the direction of gravity,the direction of the axis and the known orientation of the patient withrespect to gravity. When the patient is positioned in a secondorientation, the intra-operative computing unit is further configured toprovide surgical navigation based on the registration coordinate frame.

There is disclosed a medical navigational guidance system comprising: asensor comprising an optical sensor configured to generate opticalmeasurements and an inclinometer configured to generate inclinationmeasurements; a first target attached to an anatomy of a patientconfigured to provide positional signals in up to six degrees of freedomto the optical sensor; a second target configured to provide positionalinformation in up to six degrees of freedom to the optical sensor andconfigured to be attached to a device with a shape that defines at leastone axis, wherein the at least one axis has a known positionalrelationship with the second target; and an intra-operative computingunit. The sensor is configured to attach to an operating table. Thesensor is further configured to be held in the hand of a surgeon. Theintra-operative computing unit is configured to: receive positionalsignals of the first target from the optical sensor; receive inclinationmeasurements from the inclinometer; calculate position and orientationof the first target; calculate the direction of gravity with respect tothe position and orientation of the first target based on theinclination measurements; measure the direction of the at least one axisusing positional information provided by the second target and the knownpositional relationship between the second target and the device; andconstruct a registration coordinate frame for the anatomy of the patientbased on the direction of gravity with respect to the first target,position and orientation of the first target and the direction of theaxis.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments disclosed herein will be more fully understood from thedetailed description and the corresponding drawings, which form a partof this specification, and in which:

FIG. 1 shows some components of an electronic guidance system inaccordance with an embodiment;

FIG. 2 shows an axis frame used in registration of an of a patient tothat of the electronic guidance system for surgery in accordance with anembodiment;

FIG. 3 shows a target member removably attached to an axis frame inaccordance with an embodiment:

FIG. 4 shows labels on one of the axes of an axis frame as an examplefor clarity;

FIG. 5 shows the axis frame resting on a femur bone of a patient as anexample for clarity;

FIG. 6 is a screenshot of a representative verification feature in adisplay unit of a workstation of the electronic guidance system inaccordance with an embodiment;

FIG. 7 shows a cross-section of a sensor with optical and inertialsensing components in an electronic guidance system as an example forclarity;

FIG. 8 shows an axis frame with a single axis as an example for clarity;

FIG. 9 shows a patient positioned laterally, with a sensor of anelectronic guidance system attached to the anatomy of the patient, and aprobe to capture locations of landmarks as an example for clarity:

FIG. 10 is a screenshot of a representative bubble level graphicupdating in real-time on a display unit of a workstation of anelectronic guidance system;

FIG. 11 is a screenshot of a display unit of a workstation showingmeasurements in internal and external reference coordinate frames inaccordance with an embodiment;

FIG. 12 shows an anatomy of a patient and a sensor attached to anoperating table or bed to capture measurements from the axis frame as anexample for clarity;

FIG. 13 is a flowchart of a method for registration using a registrationdevice;

FIG. 14 is a flowchart of a method for total hip arthroplasty using anelectronic guidance system in accordance with an embodiment;

FIG. 15 is a flowchart of a method for registration using an axis frameonly in accordance with an embodiment:

FIG. 16 is a flowchart of a method for registration using an axis frameand inclination measurements in accordance with an embodiment;

FIG. 17 is a flowchart of a method for registration using inclinationmeasurements and localized landmarks in accordance with an embodiment;and

FIG. 18 is a flowchart of a computer-implemented method for registrationusing an axis frame and inclination measurements.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION

Systems, methods and devices are presented herein pertaining toanatomical registration and surgical localization during surgicalnavigation. The embodiments refer to use of an electronic guidancesystem in THA. However, a person skilled in the art will realize thatthe specification is applicable to other forms of surgery and is notmeant to be limited to THA. It is further understood that variousmethods described for performance by a computer system such asnavigational surgery may be implemented in software such as instructionsand data to configure at least one processing unit of a computer systemto perform the method. The instructions and data may be stored in adevice such as a memory (RAM, ROM, flash drive, etc.) or othernon-transitory storage device (e.g.: magnetic, optical, or other disk orstorage medium).

Several systems, methods and devices will be described below asembodiments. The scope of the claims should not be limited by theembodiments set forth in the examples, but should be given the broadestinterpretation consistent with the description as a whole.

In order to provide electronic guidance with respect to the anatomy ofthe patient in THA, the spatial coordinates of the anatomy of thepatient (e.g., the pelvis) with respect to the electronic guidancesystem are required. This step is referred to as “registration” in thisspecification. Anatomical registration pertains to generating a digitalpositional or coordinate mapping between the anatomy of interest and alocalization system or an electronic guidance system. There are multiplemethods to obtain this registration mapping or the registrationcoordinate frame. It is desirable that these methods of registration arefast, so as to not increase the duration of the surgical workflow, andsufficiently accurate. The electronic guidance system utilizes theregistration coordinate frame to intra-operatively provide clinicallyrelevant measurements to the surgeon using the system. FIG. 1illustrates an electronic guidance system 100 used in THA where a sensor102 is attached an anatomy of a patient (e.g. a pelvis 104) andcommunicates with a workstation or an intra-operative computing unit106. The pose (position and orientation) of a target 108 can be detectedby the sensor 102 and displayed on a graphical user interface (GUI) 110of the workstation 106. The target 108 may be attached to an instrument112 or to another part of the anatomy of the patient (e.g. to a femur).

Pelvic registration, particularly useful in THA, is selected as anexemplary embodiment; however, this description is intended to beinterpreted as applicable to general anatomy and in various othersurgeries.

In this disclosure, normally a sensor is attached to a bone of theanatomy of the patient or a steady surface such as an operating table. Atarget, detectable by the sensor in up to six degrees of freedom, islocated on an object being tracked, such as another bone of the anatomyof the patient, a tool, a prosthesis, etc. However, in general, thelocations of the sensor and target can be reversed without compromisingfunctionality (e.g. fixing the target on the bone or a steady surfaceand attaching the sensor to the object to be tracked), and thisdisclosure should be interpreted accordingly.

Furthermore, one skilled in the art will appreciate that the techniques,components, and methods described herein may be implemented usingdifferent tracking modalities. For example, use of traditionalstereoscopic localization cameras (e.g. the Polaris™ product fromNorthern Digital Inc. in Waterloo, ON), electromagnetic tracking systems(e.g. the Aurora™ product from Northern Digital Inc), ultrasoniclocalizers (e.g. see U.S. Pat. No. 8,000,926), mechanical localizationdevices. RF localizers, etc. are contemplated.

Reference is now made to FIG. 2, which illustrates a device 202,referred to as an axis frame that may be used to register an anatomy ofa patient. Through its shape, an axis frame 202 can define axes, such asa first axis 204, a second axis 206 and a third 208 axis. For example,an axis frame may be comprised of three orthogonal bars (204, 206, and208) that define three axes. The sensor 102 is attached to the pelvis ofthe anatomy 104 of the patient and communicates with an intra-operativecomputing unit 106 through a cable 210. The sensor may comprise anoptical sensor to track positional information of the target 108attached to the axis frame 202. This information is used to measure thedirections of the anatomical axes of a patient in order to construct theregistration coordinate frame. At the time of use, the positionalrelationship between the axes of the axis frame 202 and the target 108must be known to the intra-operative computing unit 106, either throughprecise manufacturing tolerances, or via a calibration procedure. Thisrelationship is vital to determining the registration coordinate frame.Generally, surgical grade metals are used to manufacture devices suchas, an axis frame, as these metals are biocompatible and can besterilized in a hospital setting.

Rather than have a dedicated target for the axis frame, it may beadvantageous to provide a removable target, such that the same targetmay be used to track a variety of instruments, implants and/or objects.The axis frame may have a target that is removably or integrally affixedto the axis frame and that can be tracked by the optical sensor. This isillustrated in FIG. 3, where the target 108 may be detached from thebody of the axis frame 202, and may be coupled via a repeatable mount orquick connect mechanism 302, such as the one taught in U.S. 20140275940titled “System and Method for Intra-Operative Leg Position Measurement”and filed on Mar. 15, 2013, the entire contents of which areincorporated herein by reference. The quick connect mechanism 302 isrepeatable and accurate to ensure that the pose of the target 108repeatably and accurately relates to the pose of the axis frame 202 in apre-determined mathematical relation.

In addition to the shape of the axis frame that defines the axis/axes ofinterest for the purpose of registration, clinically relevant markingsor labels may be used to define how the axis frame is intended to bealigned. In FIG. 4, for example, if a straight bar is used in an axisframe to define the anterior-posterior direction on a patient it may belabeled accordingly with an anterior label 402 and a posterior label404.

An important aspect of the design of the axis frame is that it istrackable when in alignment with the anatomy. When the axis frame isaligned with the patient, the target must be within the field of view ofthe camera or sensor. This aspect may take into accountpatient-to-patient anatomical variations, as well as variations in thepositioning of the sensor on the pelvis.

Since the axis frame requires a user to manipulate it into the correctposition with respect to the anatomy, ergonomic considerations for theuser are important. In one embodiment as illustrated in FIG. 5, a hand502 of a user is depicted holding an axis frame 202 with a contact point504 resting on a femur 506 during a pelvic registration. A membercomprising the contact point 504 may be at an additional attachment tothe axis frame 202 such that it is attached only if and when requiredduring the surgical workflow. The contact point 504 may be located atthe tip of any of the axes of the axis frame 202. The purpose of thecontact point 504 is to allow a user to manually rest the axis frame ona stable point such that the axis frame 202 is easier to manually alignwith the anatomy of interest. It is easier to align something when it ispartially stabilized. The contact point 504 may be within a surgicalwound, or outside. The location of the contact point 504 is not requiredto be repeatable.

A verification feature may be provided in the intra-operative computingunit. For example, after the registration coordinate frame has beencalculated, the axis frame may continue to be tracked as it ismanipulated by a user (e.g. a surgeon). As shown in FIG. 6, a GUI 110 ona display unit may update in real-time a current position of the axisframe relative to the registered position or coordinate frame. In thiscase, a metric, such as the three-dimensional difference in orientation,is depicted. Fewer degrees of freedom may also be depicted. Thisverification feature provides real-time feedback to the user, and allowsthe user to assess confidence in the positioning of the axis frame forregistration. The computing unit may also allow the user to re-do thestep of registration, should the user choose to do so. Although anumerical display is shown in FIG. 6, it may be preferable to include agraphical display, such as a bulls-eye graphic. The computing unit mayprovide guidance on how to move the axis frame in order to return to theoriginal registered position.

The verification feature also allows a user to verify and/or redo theregistration steps at any point during the surgical procedure. It ispreferable to perform the registration as soon as possible after thepatient has been positioned and draped for surgery, such that theorientation of the anatomy (e.g. the pelvis) is known. The patient maythen be moved (deliberately or unintentionally) as part of the surgicalworkflow without compromising the registration. Since the surgeon istypically involved in the preparation and draping, the surgeon will havea spatial awareness of the anatomical positioning of the patient withrespect to the ground or to the operating table or to any otherstationary object, even if the body of the patient is obscured bysurgical draping. Furthermore, in many surgeries, the anatomy of thepatient may shift or purposefully be moved as the surgeon may berequired or may choose to position the patient into various positions.Registering the anatomical coordinate frame of the patient as soon aspossible after patient positioning may eliminate patient shifting as asource of measurement error.

In many surgical procedures, such as THA, care is taken in patientpositioning at the beginning of surgery. For example, whether in lateraldecubitus or supine positioning, surgeons often ensure that the patientis in a known position with respect to the horizontal plane (referringto the plane orthogonal to gravity). The knowledge of the position ofthe patient with respect to the horizontal plane is often used as an aidin positioning implants. The ability to electronically measure thehorizontal plane has several advantages. This information may be used toaid anatomical registration (i.e. taking advantage of the care takenwhen positioning patients). The horizontal plane may be registered atthe commencement of the surgical procedure, with a low likelihood of theanatomy of the patient having shifted under the surgical draping.

Incorporating inclination sensing that can assist in the determinationof the horizontal plane may be accomplished, for example, by adding aninclinometer (or accelerometer) into the sensor, as depicted in FIG. 7.The sensor 102 comprises an optical sensor (a camera 704 comprising alens 706, an optical window 708, etc.) that is connected by a rigidstructure 710 to an inclinometer 712. The sensor 102 is also connectedvia a connector 714 and a cable 210 to a workstation 106. In this case,the sensor 102 provides optical and inclination measurements, bothrelated to a common frame of reference. Further discussion on how toenable this is provided below.

Often, three degrees of freedom in orientation are needed to registerthe anatomy. Inclination measurements provide two degrees of freedom inorientation. The inclination measurements may be used for constructionof the registration coordinate frame. For example, if an anatomy of apatient has a known position with respect to the horizontal plane, thesensor (attached to the anatomy or to a stable location, such as, theoperating table) measures the horizontal plane, and the intra-operativecomputing unit uses this information as part of anatomical registration.Using inclination measurements to provide up to two degrees of freedom,the third degree of freedom may be measured from an axis frame,configured to provide a single axis. As in FIG. 8, a hand 502 of a useris shown holding an axis frame 202 with a single axis 804 and a target108 attached to it. During registration, the single axis may be alignedanywhere within the plane of the final degree of freedom.

It may be the case that the anatomy of the patient has a known positionwith respect to only one degree of freedom of the horizontal plane. Inthis case, two additional degrees of freedom from an axis frame may berequired to enable registration of the anatomy. The axis frame with asingle axis and a target affixed to it may define at least two degreesof freedom in orientation. The registration coordinate frame may then beconstructed by utilizing all three degrees of freedom.

Furthermore, it may be beneficial to generate redundant informationrequired for the registration step. Redundant information can beobtained from a full registration using an axis frame and inclinationmeasurements to capture the same degrees of freedom. Redundantregistration information may be beneficial for error checking, or forusing an optimization routine to register the anatomy of the patientbased on the aggregate information. This information, in the form of ametric, may be displayed to the user or may be used to represent theconsistency between the measurements obtained from the inclinationsystem and the optical sensor.

According to a preferred method wherein inclination measurements andoptical measurements are used to define a registration, the inclinationmeasurements and the optical measurements may be captured or measuredsubstantially contemporaneously.

An axis may also be defined by capturing (or “localizing”) two discretepoints. A device such as a probe, with a tip that is in a knownpositional relationship with the target affixed to it, may be used todetermine the location of two or more anatomical features of interest.The position of the tip of the probe may be captured by the electronicguidance system as a part of the registration of the anatomy. The twodiscrete points (in three-dimensional space) localized by the probedefine a vector (analogous to how any one axis of an axis frame definesa vector). For example, the discrete point may be the ASIS (anteriorsuperior iliac spine) of a pelvis, which is a commonly utilizedanatomical location for registration.

There are various surgical approaches in THA, such as the posteriorapproach, anterior approach, etc. that require the patient to bepositioned in lateral decubitus or supine. The anterior pelvic plane(APP) of the anatomy is comprised of both ASIS locations and the pubicsymphysis, and is often used for registration of the pelvis in differentsurgical approaches. Accessing points that define the anterior pelvicplane can be challenging when a patient is positioned in lateraldecubitus, since the location of the contralateral ASIS is obscured anddifficult to access for the surgeon. However, if the pelvis ispositioned substantially vertically with respect to the operating tableor the horizontal plane, this obviates the need to access thecontralateral ASIS. It is sufficient to localize two points, such as,the operative ASIS, and the pubis using a probe. These points lie in thefrontal plane of the pelvis, and, in combination with inclinationmeasurements (which provide the third degree of freedom), the pelvicregistration coordinate frame may be constructed. FIG. 9 illustrates asensor 102 attached to the pelvis 104 of the patient when the patient ispositioned laterally. The target 108 attached to a probe 902 can be usedto localize landmarks like the operative ASIS 904 and the pubis 906 orlocations within the acetabulum 908. The probe 902 is illustrated to beunitary with the target 108. However, this is not a limitation of thisembodiment. The target 108 may be removably attached to the probe 902.The workstation measures the position and orientation of the tip of theprobe 902 using positional information from the target 108 to determinethe location of the landmarks.

In one embodiment, the inclination measurements of the sensor areprovided to the surgeon in real-time to track patient motion during theprocedure. These measurements may be provided to a surgeon (e.g.persistently) via the GUI on the display unit. As illustrated in FIG.10, for example, the measurements may be conveyed as a bubble levelgraphic 1002 where the graphic may be persistently in real-time orselectively displayed, in addition to other GUI content 1004. Theinclination measurements may be displayed relative to the measurementscaptured during registration such that the bubble 1006 is centered inthe graphic 1002 when the current inclination matches the inclinationmeasured at registration. Furthermore, the direction of the bubble level1006 may utilize the registration coordinate frame such that the currentinclination is expressed with respect to the anatomical directions ofthe body of the patient. As an example, if the bubble moves to the righton the screen, this may have a physical relationship to how the patientmay have shifted.

In order to provide inclination measurements, an accelerometer may beintegrated within the sensor, as shown in FIG. 7. The optical sensor ofthe sensor comprises an optical window 708, a camera 704 comprising alens 706. The accelerometer measurements are combined with opticalmeasurements using techniques known in the art of sensor fusion, suchthat measurements are provided with a common frame of reference. A rigidstructure 710 exists between the location of the camera and theaccelerometer, thus creating a rigid mechanical relationship. Thisrelationship is unique for each physical device and is used by theworkstation when both the accelerometer 712 and camera 704 communicatemeasurements to it by any means. e.g. wired through a cable 210,wireless, etc. The workstation may use this relationship to aligninclinometer coordinate values to the optical coordinate values, anddisplay further calculations in the same frame of reference.

In addition or alternative to accelerometers, other sensing componentsmay be integrated to assist in registration and/or pose estimation. Suchsensing components include, but are not limited to, gyroscopes,inclinometers, magnetometers, etc. It may be preferable for the sensingcomponents to be in the form of electronic integrated circuits.

Both the axis frame and the accelerometer may be used for registration.The optical and inclination measurements captured by the system rely onthe surgeon to either accurately position the patient, or accuratelyalign the axis frame along the axis/axes of an anatomy of a patient, orboth. It may be desirable to provide further independent information foruse in registering the anatomy of the patient. For example, in THA, thenative acetabular plane may be registered by capturing the location ofat least three points along the acetabular rim using a probe attached toa trackable target. When positioning implants with respect to thepelvis, information may be presented with respect to bothregistrations—one captured by the workstation from optical measurementsof the axis frame and inclination measurements (primary registrationcoordinate frame), and the other captured by the workstation using thereference plane generated from the optical measurements of the localizedlandmarks on the acetabular rim of the patient (secondary registrationcoordinate frame)—either in combination, or independently.

FIG. 11 shows a GUI on a display unit. In this embodiment, the interfacesplits the screen into two sections—an Internal Reference 1102 and anExternal Reference 1104. The Internal Reference 1102 presents a frame ofreference with respect to the internal acetabular landmarks that wereindependently captured in the construction of the registrationcoordinate frame as the native anatomy of the patient. A graph 1106 onthe GUI displays a bulls-eye indicator 1110 that represents the nativeacetabulum. The External Reference 1104 presents data to the surgeon ina registration coordinate frame defined by the measuring of thehorizontal plane and/or axis frame. The surgeon may use their clinicaljudgment in interpreting the data and taking appropriate action. In thisexample, the clinical measurements presented are for real-timeacetabular cup alignment in THA.

In the previous embodiments, a sensor has been attached to the anatomyof the patient that is to be registered for the surgical procedure. Eachof the previous embodiments may be modified by changing the location ofthe sensor to another location from which it can detect the position andorientation of one or more targets. For example, the sensor may beattached to an operating table, held in the hand of a surgeon, mountedto a surgeon's head, etc. This embodiment is illustrated in FIG. 12. Thesensor 102 is depicted attached to an operating room table 1202. A firsttarget 1204 may be attached to the pelvis 104 of the patient, and asecond target 1206 may be attached to a registration device (probe 902or axis frame 202). The sensor 102 captures the position and orientationof both targets. The workstation calculates a relative measurement ofposition and orientation between both targets. In addition, the sensor102 captures the inclination measurements, and the position andorientation of the first target 1204 attached to the anatomy of thepatient. The workstation then calculates the direction of the gravitywith respect to the first target 1204. Using the relative posemeasurement between both targets, and the direction of gravity withrespect to the first target 1204 attached to the anatomy of the patient,the workstation can construct the registration coordinate frame.

An exemplary method of use as shown in the flowchart of FIG. 13 mayinclude the following: at step 1302, a patient is positioned, theposition being known to the surgeon. At step 1304, a sensor is rigidlyattached to the pelvis at an arbitrary position and orientation withrespect to the anatomy. At step 1306, an axis frame, with a trackabletarget, is tracked by the sensor. At step 1308, when the axis frame ispositioned in alignment with the known position of the patient's anatomyby the surgeon, step 1310 is carried out the computing unit to capturethe pose of the axis frame by. This pose is used to compute aregistration coordinate frame between the sensor and the anatomy. Atstep 1312, the axis frame is removed and/or discarded, and subsequentpositional measurements of the localizer system are calculated on thebasis of the registration coordinate frame.

Various methods, devices and systems for anatomical registration arepresented herein. The following provides an exemplary workflowillustrating their practical usage in the context of THA. These stepsare to provide an exemplary workflow, and not all of the steps aremandatory. For example, if a surgeon is not interested in leg positionmeasurement, the corresponding steps may be omitted.

As shown in FIG. 14, the flowchart illustrates the steps involved in theoverall workflow of TI-IA. The first step 1402 involves preparing apatient for surgery, including positioning and draping. The surgerybegins at step 1404 in which the surgeon (in no particular order)attaches the sterile sensor to the pelvis of the patient, registers thepelvis, exposes the hip joint, and captures a baseline leg positionmeasurement and native hip center of rotation position. Those skilled inthe art will understand that there are numerous methods, systems anddevices available to register the patient and obtain the baselinemeasurements, some of which are described in the disclosure herein. Thenext step 1406 is to dislocate the hip joint of the patient. This isfollowed by step 1408 for registration of internal referencinglandmarks, such as, on the acetabular rim. The surgeon then reams theacetabulum at step 1410 to create the surface that will receive theacetabular implant. The surgical navigation system is then used to alignthe acetabular prosthetic under guidance from the system at step 1412,by tracking the position and/or orientation of the acetabular cup,displaying measurements to the surgeon via the workstation GUI. Themeasurements may be expressed relative to one or both of the pelvicregistration and the internal reference landmarks from the acetabularrim, and selecting a suitable alignment and implanting the acetabularcup.

At step 1414, the surgeon then prepares the femur of the patient andperforms trial reductions. During the trials, at step 1416, the surgeoncaptures a new hip center of rotation position with the prosthetic inplace. Finally, at step 1418, the workstation measures and displayschange in leg position and change in hip center of rotation position,and the measurements are presented to the surgeon according to theregistration coordinate frame.

In an embodiment, the axis frame can be used in THA as described belowin the detailed workflow options for pelvic registration. The method isdescribed in FIG. 15. Using an axis frame at step 1502, the anatomy ofthe patient can be registered by bringing the axis frame, with thetarget attached to it, in alignment with the pelvis of the patient whilethe target is in the field of view of the optical sensor. At step 1504,once the user is satisfied that the axis frame is positionedappropriately with respect to the anatomy of the patient, the userinitiates a capture of the position and orientation of the target in upto six degrees of freedom. This could be done, for example, through ahuman user interface, such as, a button. At step 1506, theintra-operative computing unit utilizes this information and computes aregistration coordinate frame for the patient.

Reference is now made to FIG. 16, which illustrates a method ofregistration. The inclination measurements captured from an inclinometerin the sensor can provide additional measurements to the intra-operativecomputing unit for constructing the registration coordinate frame. Atsteps 1602 and 1604, measurements from the axis frame while it ispositioned in alignment with the anatomy of the patient are captured andthe intra-operative computing unit utilizes these measurements tocompute one or two degrees of freedom of the registration measurement.At step 1606, the final degree(s) of freedom is/are captured from theinclinometer when the patient is positioned laterally on an operatingtable with his/her pelvis orthogonal with respect to the ground. Sincethe inclinometer can be housed within the optical sensor, there may be ahuman user interface, such as a button, to capture the optical andinclination measurements simultaneously. The two measurements can alsobe captured in distinct steps. Using both sets of measurements, at step1608, the intra-operative computing unit can construct the registrationcoordinate frame.

Reference is now made to FIG. 17. Instead of using an axis frame todetermine an axis of the body of the patient, at step 1702, a probe withan attached target that can be tracked by the optical sensor may be usedto localize at least two anatomical landmarks that lie along ananatomical plane (e.g. frontal plane) of the pelvis, e.g.: an operativeASIS and the pubic symphysis. The location of the probe tip is in aknown positional relationship with respect to the target. At step 1704,when localizing landmarks, the intra-operative computing unit capturesthe location of the tip of the probe as it is placed on an anatomicallandmark and the optical sensor captures the positional information fromthe target. While the patient is positioned laterally, i.e. orthogonalto the floor, and the sensor is attached to the body of the patient suchthat the sensor is upright, inclination measurements are captured (suchthat the inclination measurements define a plane that represents thesagittal plane of the patient) at step 1706. The intra-operativecomputing unit is then able to compute the registration coordinate framein three degrees of freedom based on the two localized landmarks andinclination measurements at step 1708.

Reference is now made to FIG. 18. A computer-implemented method 1800 fora medical navigation guidance system is shown in a flowchart. The methodis capable of, at step 1801, measuring a direction of gravity using asensor 102, the sensor comprising an optical sensor and an inclinometer,attached to an anatomy of a patient positioned in a known orientationwith respect to gravity; at step 1802, measuring, by at least oneprocessing unit, a direction of an axis of a device 202, the device 202having a shape defining at least one axis using positional informationin up to six degrees of freedom provided by a target 108 to the opticalsensor, and a known positional relationship between the target 108 andthe device 202; and at step 1803, constructing, by at least oneprocessing unit, a registration coordinate frame to register, duringsurgery, the anatomy of the patient based on the direction of gravity,the direction of the axis and the known orientation of the patient withrespect to gravity.

Accordingly, it is to be understood that this subject matter is notlimited to particular embodiments described, and as such may vary. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the teachings herein. Any recitedmethod can be carried out in the order of events recited or in any otherorder which is logically possible.

What is claimed is:
 1. A system comprising: a sensor configured toattach to an anatomy of a patient positioned in a known orientation withrespect to gravity, and comprising an optical sensor to generate opticalmeasurements and an inclinometer to generate inclination measurements; atarget configured to provide positional information to the opticalsensor, the optical sensor generating the optical measurements using thepositional information in up to six degrees of freedom; a deviceattached to the target, the device having a shape defining at least oneaxis, wherein the at least one axis is in a known positionalrelationship with the target; and an intra-operative computing unit incommunication with the sensor, the intra-operative computing unitconfigured to: measure a direction of the at least one axis using theoptical measurements from the sensor and the known positionalrelationship between the target and the device; measure a direction ofgravity based on the inclination measurements; construct a registrationcoordinate frame to register the anatomy of the patient during surgeryto provide surgical navigation based on the direction of gravity, thedirection of the axis and the known orientation of the patient withrespect to gravity.
 2. The system of claim 1 wherein the device isremovably attached to the target.
 3. The system of claim 1 wherein theanatomy of the patient is a pelvis.
 4. The system of claim 1 wherein thesurgery is a Total Hip Arthroplasty.
 5. The system of claim 1 whereinthe intra-operative computing unit is further configured to calculate inreal-time a difference in the optical measurements in at least onedegree of freedom provided by the optical sensor with respect to theregistration coordinate frame and to provide the difference for displayby a display unit.
 6. The system of claim 1 wherein the intra-operativecomputing unit constructs the registration coordinate frame usingredundant measurement information wherein the redundant measurementinformation is used to compute a metric representing the consistencybetween the inclination measurements and optical measurements, and theintra-operative computing unit is further configured to provide themetric to a display unit for displaying to a surgeon.
 7. The system ofclaim 1 wherein the sensor is configured to generate opticalmeasurements and inclination measurements relative to a common frame ofreference.
 8. The system of claim 7 wherein the intra-operativecomputing unit is configured to construct the common frame of referenceusing a rigid mechanical relationship between the optical sensor and theinclinometer.
 9. A system comprising: a sensor configured to attach toan anatomy of a patient comprising an optical sensor to generate opticalmeasurements and an inclinometer configured to generate inclinationmeasurements; a target configured to provide positional information tothe optical sensor, the optical sensor generating the opticalmeasurements using the positional information in up to six degrees offreedom; a probe attached to the target, the probe having a tip, whereinthe tip is in a known positional relationship with the target; and anintra-operative computing unit in communication with the sensor, theintra-operative computing unit configured to: determine a location oftwo or more anatomical features of the patient using opticalmeasurements of the sensor and the known positional relationship betweenthe target and the tip of the probe; calculate a direction of at leastone axis defined by the location of the two or more anatomical features;measure a direction of gravity based on the inclination measurements;and construct a registration coordinate frame to register during surgerythe anatomy of the patient based on the direction of gravity and thedirection of the axis.
 10. The system of claim 9 wherein the probe isremovably attached to the target.
 11. The system of claim 9 wherein theanatomy of the patient is a pelvis.
 12. The system of claim 9 whereinthe surgery is a Total Hip Arthroplasty.
 13. The system of claim 11wherein the two anatomical features lie on the anterior pelvic plane ofthe patient.
 14. The system of claim 11 wherein the intra-operativecomputing unit is further configured to generate a secondaryregistration coordinate frame by localizing three anatomical features onthe acetabular rim of the patient.
 15. The system of claim 14 whereinthe system is configured to provide navigational guidance based on theregistration coordinate frame and the secondary registration coordinateframe.
 16. A computer-implemented method comprising: measuring, by atleast one processing unit, a direction of gravity using a sensor, thesensor comprising an optical sensor and an inclinometer, attached to ananatomy of a patient positioned in a known orientation with respect togravity; measuring, by at least one processing unit, a direction of anaxis of a device, the device having a shape defining at least one axisusing positional information in up to six degrees of freedom provided bya target to the optical sensor, and a known positional relationshipbetween the target and the device; and constructing, by at least oneprocessing unit, a registration coordinate frame to register duringsurgery the anatomy of the patient based on the direction of gravity,the direction of the axis and the known orientation of the patient withrespect to gravity.
 17. The method of claim 16 wherein the patient ispositioned in a second orientation and the intra-operative computingunit is further configured to provide surgical navigation based on theregistration coordinate frame.
 18. A system comprising: a sensorcomprising an optical sensor configured to generate optical measurementsand an inclinometer configured to generate inclination measurements; afirst target attached to an anatomy of a patient configured to providepositional signals in up to six degrees of freedom to the opticalsensor; a second target configured to provide positional information inup to six degrees of freedom to the optical sensor and configured to beattached to a device with a shape that defines at least one axis,wherein the at least one axis has a known positional relationship withthe second target; and an intra-operative computing unit configured to:receive positional signals of the first target from the optical sensor;receive inclination measurements from the inclinometer; calculateposition and orientation of the first target; calculate the direction ofgravity with respect to the position and orientation of the first targetbased on the inclination measurements; measure the direction of the atleast one axis using positional information provided by the secondtarget and the known positional relationship between the second targetand the device; and construct a registration coordinate frame for theanatomy of the patient based on the direction of gravity with respect tothe first target, position and orientation of the first target and thedirection of axis.
 19. The system of claim 18 wherein the sensor isconfigured to attach to an operating table.
 20. The system of claim 18wherein the sensor is configured to be held in the hand of a surgeon.